Precision level measurement and control apparatus

ABSTRACT

The present system includes a plummet or weight which moves in response to gravity to come to rest on the top of the material, in the case of a granular or particulate solid, whose level is being measured, or to determine the upper surface, in the case of a liquid, whose level is being monitored. The plummet is connected to a support menas, such as a perforated tape, which in turn is coupled to drive a counter device. When the plummet stops moving downward the level can be read as a function of shaft position such as by a counter device, a shaft motion transmitter, pulser, or shaft encoder. In addition the support means is coupled to a take-up means which lifts the plummet upward in accordance with a periodic energization of the take-up means. The energization of the take-up means is controlled by a logic circuit which determines the period for the take-up action and the gravity probe.

Unite States Patent 1191 Taylor 1 Apr. 24, 1973 PRECISION LEVELMEASUREMENT AND CONTROL APPARATUS Primary Examiner-Benjamin Dobeck 75Inventor: William s. Taylor, Drexel Hill, Pa. wobensmthi [73] Assignee:FIC Industries, Inc. [57] ABSTRACT [22] Filed: June 17, 1971 The presentsystem includes a plummet or weight which moves in response to gravityto come to rest on [21] Appl 153357 the top of the material, in the caseof a granular or particulate solid, whose level is being measured, or to52 us. Cl. ..318/482, 73/313, 73/321, determine the upper Surface in thecase of a liquid,

318/642 whose level is being monitored. The plummet is con- [51] Int.Cl. ....G05d 9/00 to a PP menas, u h as a perforated tape, [58] Field ofSearch ..318/482 642' wh'ch in tum i a device 73/304 C 313 321. 33/126When the plummet stops moving downward the level I can be read as afunction of shaft position such as by a counter device, a shaft motiontransmitter, pulser, or [56] Refer-em Cite? shaft encoder. In additionthe support means is cou- UNITED STATES PATENTS pled to a take-up meanswhich lifts the plummet upward in accordance with a periodicenergization of the 3,473,380 10/1969 Mayer et a1 ..73/3()4 C take-upmeans. The energization of the take-up means 3,551,740 2/1970 Manners Xis controlled by a logic circuit which determines the 2,632,026 Mesh atI 8/482 X period for the take-up action and the gravity probe. 3,836,7395/1958 Mesh 318/482 X 3,473,381 10/1969 Allen, Jr ..73/313 10 Claims, 9Drawing Figures Patented April 24, 1973 4 Sheets-Sheet l lNl/ENTOI? F162BY k A r ram Er Pat ented April 24, 1973 4 Sheets-Sheet 2 I INVENTORWILL/AM s. TAYLOR A 7' TORNEY Patented April 24, 1973 3,729,667

4 Shets-Sheet 4 FIG. 7

INVENTOR WILLIAM S. TAYLOR.

ATTORNEY PRECISION LEVEL MEASUREMENT AND CONTROL APPARATUS BACKGROUND OFTHE INVENTION 1. Field of the Invention The present invention relates tosolid or liquid level measuring devices. In particular the presentinvention relates to a level measuring device which continually probesor samples the level of the material whose level it is monitoring.

2. Description of the Prior Art In the prior art there have been effortsmade to employ a probe technique by using resonant circuits whose signalstrength varied with the proximity of the level of a liquid and othermechanical or electric detecting systems that do not provide accuracycomparable to that obtained with the present invention. Thesearrangements employ very sophisticated and costly circuits andservomotor systems. The present invention provides the advantages ofelectronic controls but with a simplicity of logic to enable the systemto be electronically" accurate but relatively economic.

SUMMARY OF THE INVENTION In accordance with the invention a precisionlevel measuring and control device is provided for liquids or solidswhich includes a plummet or weight movable downwardly in response togravity to come to rest on the top of the material, in the case of agranular or particulate solid, whose level is being measured, or todetermine the upper surface, in the case of a liquid, by conductivity ora float switch whose level is being monitored, whereby the plummet islowered by a driven mechanical movement and the level surface isdetected by conductivity or float action. The plummet is connected to asupport means, such as perforated tape, which in turn is coupled todrive a counter device. When the plummet stops moving downward the levelcan be read as a function of shaft position such as by a counter device,a shaft motion transmitter, pulser or shaft encoder. In addition, thesupport means is coupled to a take-up means which lifts the plummetupward in accordance with a periodic energization of the take-up means.The energization of the take-up means is controlled by a logic circuitwhich determines the period for the take-up action and the gravityprobe.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of thepresent invention will be better understood from the followingdescription taken in conjunction with the drawings wherein:

FIG. I is a pictorial schematic of the mechanical part of the systemembodiment used to monitor solids;

FIG. 2 is a circuit schematic of the logic circuitry employed to controlthe operation of the embodiment shown in FIG. 1; I

FIG. 3 is a pictorial schematic of the mechanical part ofthe systemembodiment used to monitor liquids;

FIG. 4 is a circuit schematic of the logic circuitry employed to controlthe operation of the embodiment shown in FIG. 3;

FIG. 5 is a circuit schematic of the logic circuitry to monitor liquidswith plummet in FIG. 6;

FIG. 6 is a fragmentary view showing a modified form of plummet;

FIG. 7 is a diagramatic view of another form of plummet with two probesfor use with conductive liquids;

FIG. 8 is a diagrammatic view of another ball shaped plummet; and

FIG. 9 is a more detailed view of the plummet of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there isshown a plummet 11 which is held by a perforated strap 13. In thepreferred embodiment the weight or plummet 11 is fabricated fromstainless steel and weighs approximately 2% lbs. It should be understoodthat the plummet could be fabricated from many other materials such asplastic, brass, or other solid materials which have little tendency tobecome chemically active with the material whose level is beingmonitored. It should also be understood that the support means orperforated strap 13. could be any one ofa number of support means suchas a chain, tape, cable or the like which is formed to be engageable andpreferably positively engageable with a drive means to drive a counteror readout device.

In the embodiment shown in FIG. 1, the perforated strap 13 engages thesprocket 15 which is mounted on the shaft 17. When the sprocket 15 turnscounterclockwise in response to the plummet 11 traveling downward (bythe force of gravity) the shaft 17 will also rotate counterclockwisethereby causing the counter 19 to decrement or go to a lowernumber.

It follows that if the plummet 11 travels further downward into thetank, bin or other receptacle, the level of the material must berelatively low and a smaller value must be shown at the window of thecounter.

The counter 19 in the preferred embodiment is a Veeder Root counteralthough many other types of mechanical counters, pulsers, shaftencoders or other devices could be used. When the plummet 11 comes torestion the solid material the counter 19 will no longer be changingvalues, as viewed by the user, and hence the level of the solid materialwill be determined by viewing the value shown on the read out device.

When the plummet 11 is to be raised from the material for a probingaction the motor 21 is energized. The shaft 23 of the motor 21 iscoupled to a take-up reel 27. A friction brake 25 is carried on theshaft 23. When the motor 21 is energized and when the brake 25 is notclosed (to accomplish a braking action), the take-up reel 27 will bedriven clockwise and the perforated strap 13 will be wound onto thetake-up reel 27 thereby lifting the plummet 11.

The brake 25 is designed to remain open (no braking action) in responseto the solenoid 29 being energized. In other words, if the solenoid 29is energized the motor 21 can drive the take-up reel 27. However, if thesolenoid 29 is deenergized, the brake 25 closes and by friction gripsthe disc 31 to keep the shaft 23 from turning. The disc 31 is alsomounted for rotation with the shaft 23.

When the motor is deenergized, gravity of probe 11 will be sufficient todrive motor 21 in a free counterclockwise rotation. However, saidrotation will be braked partially by capacitor 83. Said capacitor andmotor inertia and friction are selected so that the probe rate issufficient to free wheel motor and overcome braking action of capacitor83. However, when the probe comes to rest on a solid material, brakingforce of capacitor 83 will be greater than inertia of motor and willprevent shaft from turning within a short time interval. Also the timingcircuit is so selected to permit follow-up of changing level in such amanner that if the level of the solid is lowering there is enough timefor the probe to be lifted from the surface, the motor to bedeenergized, the plummet to lower itself and return past its formerlevel to the lower level. Also, on an increasing level condition thetiming is so selected that the plummet 11 can be lifted and relowered ata pace faster than the rising level during the cycle.

A preferred circuitry which controls the motor 21 and the solenoid 29 isshown schematically in FIG. 2. The power is applied to the terminals 33and 35. when the switch 37 is closed to turn the system on, the switch39, which is mechanically linked to switch 37, is

the system is turned off, the brake 25 is held open and the motor 21 isable to run freely.

It will be noted that there is a transformer 49 whose primary winding 51is connected across the terminals 33 and 35. The transformer 49 is astep down transformer and in the preferred embodiment provides 24 voltsof alternating current voltage on the secondary winding 53. It should beunderstood that other voltages can be employed on the secondarywinding53. The voltage developed on the secondary winding 53 is appliedto the timing circuit as will be explained.

During the positive half cycle, i.e., when there is a positive voltageat terminal 55 and a negative voltage at terminal 57 there will becurrent passing through the diode 59, the resistor 61, to charge thecapacitor 63, through the normally closed relay contacts 64. Thecapacitor 63 cannot discharge during the negative half cycle because thenormally open relay contacts 66 block one path of discharge and theZener diode 69 initially blocks another path of discharge. When thecapacitor 63 is charged sufficiently, the Zener diode 69 will conductwhich in turn biases the silicon controlled rectifier 71 causing thelatter to conduct during each positive half cycle that it is so biased.Once the silicon controlled rectifier 71 conducts, it will continue toconduct until the power signal swings negative. Hence during the halfcycle that the silicon controlled rectifier 71 conducts the relay 73 isenergized and the capacitor 75 is fully charged. During the negativehalf cycles the capacitor 75 will commence to discharge and keep therelay coil 73 energized to hold the relay contacts in their activatedstates. When the relay 73 is energized, the relay contacts 65 are closedthus completing circuit continuity for the lower timing circuit. At thesame time the relay contacts 67 are opened thereby permitting thecapacitor 68 to commence charging.

part of the relay 73 array. Hence when relay 73 is deenergized thecontacts 77 are closed and there is an alternating currentvoltage acrossthe motor winding 79. Accordingly the motor 21 is energized to lift theplummet 11. The capacitor 83 is a small capacitor which provides twophased operation of the motor to drive the motor 21 in an upwarddirection.

When the relay 73 is energized the normally closed contacts 77 areopened and the power to the motor windings 79 and 81 is terminated.

I At the same time the normally open relay contact 85 are closed and thecapacitor 83 discharges through the winding 81 to dynamically brake themotor 21 which is rotating counterclockwise because of the plummet 11moving downward under the force of gravity.

It should be understood that the relay 73 will remain energized throughfiring the silicon controlled rectifier 71- on the positive half cyclesand discharging the capacitor 75 on the negative half cycles for as longas the relay contacts 64 remain closed. It should also be understoodthat the motor 21 will be energized to lift the plummet l1 upward for aslong a period as it takes the capacitor 63 to becomecharged sufficientlyto fire the Zener diode 69.

When the relay 73 becomes energized the relay contacts 65 become closedand the relay contacts 67 are opened. Accordingly, the capacitor 68commences charging on the positive half cycles through the diode 87 andthe resistor 89. When sufficient charge has been developed across thecapacitor 68, the Zener diode 91 will conduct thereby biasing thesilicon controlled rectifier 93 so that it conducts. When the siliconcontrolled rectifier 93 conducts, the relay 95 is energized and thecapacitor 97 is fully charged. The operation is similar to the operationdescribed with the upper timing circuit. On each positive half cyclesthe silicon con-. trolled rectifier 93 will conduct, and on eachnegative half cycle the capacitor 97 will discharge through the relaycoil 95 hence keeping the relay 95 energized for as long as the relaycontacts 65 are held closed.

However, the energization of the relay 95 ,is short lived because oncethe relay 95 is energized the relay contacts 64 are opened therebyterminating the energization of relay 73. When relay 73 becomesdeenergized the relay contacts 65 are opened and the energization ofrelay 95 is terminated. It should be noted 5 during the last circuitconsideration that when relay 95 becomes energized the relay contacts 66are closed to discharge the capacitor 63 thereby making the upper timingcircuit ready for the next cycle of operation. Similarly when relay 73becomes deenergized the contacts 67 become closed and the capacitor 68is discharged to make ready for the next cycle of operatron.

If the circuit operation is considered it will be apparent that whilethe capacitor 63 is being charged to a point where it will cause relay73 to become energized by firing Zener diode 69 and by firing siliconcontrolled rectifier 71, the motor 21 will be energized thus lifting theplummet 11. When the relay 73 is energized the motor 21 is no longerdriven and the plummet l1 drives the motor shaft 23 and the countershaft 17 in the-opposite direction for as long a period as it takes thecapacitor 68 to charge to a point where it causes relay 95 to beenergized. Obviously if the plummet 11 comes to rest on the solidmaterial before the capacitor 68 is sufficiently charged, the motorshaft and the counter shaft 17 will no longer be rotatedcounterclockwise and hence the counter 19 will be at rest. Actually thecapacitor 68 is chosen to permit the plummet 11 to come to rest so thatthe read out at the counter 19 or otherwise is in a steady state and thelevel of the material can be determined.

Referring now to FIG. 3 there is shown a pictorial schematic of themechanical part of an embodiment which is to be used in monitoring thelevel of liquids. In FIG. 3 there is a counter 19 which is similar tothe counter 19 in FIG. 1, a drive motor 21 which is similar to the drivemotor 21 in FIG. 1, a motorshaft 23, a disc I 31 coupled thereto, abrake 25, and a solenoid 29 all of which are similar devices to thedevices shown in FIG. 1 and therefore bear the same identificationnumerals. The probe or plummet 101 in FIG. 3 is a probe which is usedfor detecting the level or levels of a conductive liquid. The perforatedstrap or tape 103 comprises several strips of metal extruded in aplastic and the metal strips are electrically connected to the probe101. The sprocket 105 and the take-up wheel 107 are electricallyinsulated from the tape and the shafts. The probe 101 has electricalinsulation along the outside. In addition there is a slip ring 28 on thetake up wheel shaft 23 with a brush 98 engaging the ring 28 to provide Ian electrical path from ground through the liquid in the tank to thecontrol circuit being connected to the slip ring 28.

As in the embodiment shown in FIG. 1 the solenoid 29 when energized willkeep the brake open and thereby permit the drive motor 21 to drive thetake up wheel 107 to pull the probe 101 up and away from the liquid. Ifthesolenoid 29 becomes deenergized the brake 25 will close and, throughmechanical braking friction, grip the disc 31 thereby holding the takeup wheel from moving. Electrical braking of motor 21 could also beemployed. As was also true in the embodiment shown in FIG. 1,.when theperforated tape passes over the sprocket 10S it drives the shaft 17 4which will decrement when the probe 101 is going downward in the tankand increment when the probe 101 is moving upward. As will become moreapparent in the following description in connection with FIG. 4, theprobe 101 is lowered not by gravity but by driving the motor 21 in adownward direction or the counterclockwise direction until the probe 101comes in contact with the conductive liquid. When the probe 10] comes incontact with the conductive liquid the electrical circuitry connectedthereto is held at ground potential and this puts the timing circuits inoperation. At the same time the solenoid 29 is deenergized to hold theprobe 101 at that level thus enabling the user to read the level of theliquid as shown on the face of the counter 19. In FIG. 4 the circuitrywhich effects the foregoing operation is shown. Initially the switch 107must be closed in order to provide the power which is applied to theterminals 109 and 111 to the circuit. When the switch 107 is closedthere is electrical current through the normally closed relay contacts113 through the down winding 115 of the motor 21 to the other side ofthe line. Hence the motor 21 attempts to drive the probe 101 downwardtoward the liquid. At the same time there is current through thenormally closed relay contacts 113, through the normally closed relaycontacts 117, through the solenoid winding 119 to the other side of theline thereby energizing the solenoid 29 keeping the brake 25 disengaged.

Simultaneously there is an a.c. signal applied to the primary winding121 of the transformer 123. The transformer 123 is a step downtransformer as was the transformer 49 and hence there is a lower voltagedeveloped at the secondary winding 125. Initially the probe 101 is beinglowered by the motor operation of the motor 21 as just described andwhen the probe 101 reaches the conductive liquid it provides a groundpotential at the terminal 127. It should be understood that the line 129represents the perforated tape 103.

When the terminal 127 becomes grounded the silicon controlled rectifier131 becomes biased and therefore turned on during the positive halfcycle, i.e., when thevoltages are as shown on the secondary winding inthe figure. Accordingly, the silicon controlled rectifier 131 conductsto energize the relay 133 and at the same time charge the capacitor 135.As was described in connection with the earlier circuits, during thenegative half cycles the capacitor 135 discharges through the relay coil133 thereby keeping the relay energized. .For each succeeding positivecycle the silicon controlled rectifier 131 conducts as long as the probe101 is resting in the conductive liquid.

When the relay 133 becomes energized, the relay contacts 113 openthereby terminating the power to the down winding 115 while the normallyopen relay contacts 138 close. At the same time the power is terminatedto the solenoid winding 119 and the brake 25 acts to hold the take upwheel in a fixed position. Additionally, at the same time,,of course,the sprocket 105 has been moved to decrement the counter 119 so that theuser can view the value through the counter window and determine thelevel of the liquid.

The lower timing circuit is also put into operation with theenergization of the relay 133. When the relay 133 becomes energized, therelay contacts 137 are closed and hence there is current flow during thenegative half cycles (which actually provides a voltage as shown betweenthe terminals 139 and 141 in the drawing) from the terminal 139, throughthe diode 143, through the resistor 145, to charge the capacitor 147.The energization of the relay 133 opens the relay contacts 149 and hencethere is no discharge path for the capacitor 147 at this time.Accordingly there is 21 voltage developed on the capacitor 147 and whenthis voltage is sufficiently high, the Zener, diode 151 conducts therebybiasing the silicon controlled rectifier 153 which will conduct duringthe negative half cycles (as just defined). When the silicon controlledrectifier 153 conducts, the relay 155 will be energized and thecapacitor 157 will be fully charged. As was described in connection withthe relays 73, 95 and 144, during the half cycles when proper energizingpotential is not applied across the relay, the capacitor 157 willdischarge Accordingly, there is now current flow through the normallyopened contacts 138 and 161 to the up winding 163 to cause the motor 21to rotate in a clockwise direction thereby lifting the probe 101 fromthe conductive liquid. It should be noted that closing contacts 159enables the brake solenoid winding 119 to be energized. When the motor121 is energized in the upward direction, the probe 101 is lifted fromthe conductive liquid and hence the terminal 127 is no longer at groundpotential. During the following negative half cycle the conduction ofthe silicon controlled rectifier 131 is terminated and hence the relay133 becomes deenergized.

When the relay 133 is deenergized the normally closed relay contacts 113once again become closed and the normally open relay contacts 138 onceagain become opened. With the action of the last two sets of relaycontacts, it becomes apparent that with the closing of the normallyclosed relay contacts 113 the down winding 115 will become energized andhence the motor would tend to drive downward. However, with the openingof the relay contacts 138 the circuit path through the relay contacts138, 161, 159 to the solenoid winding is broken and hence the brakeholds the take up wheel against this tendency to drive the motorownward.

With the deenergization of the relay 133, the contacts 137 will onceagain become opened and hence the relay 155 will become deenergized.When the relay 155 becomes deenergized the normally closed relaycontacts 117 return to their normally closed condition thereby providinga current flow through the normally closed relay contacts 113, throughthe normally closed relay contacts 117, through the solenoid 119 to theother side of the line thereby energizing the solenoid 29 and permittingthe motor 21 to move the probe downward. In actual operation there is avirtual overlap between the transfer of the energization of the solenoidfrom the circuit path through the normally closed contact 117 and thecircuit path through the normally opened contact 159 so that the motor21 responds to the change of direction in accordance with thedeenergization of the relay 133.

The capacitor 164 is provided in the circuit to provide two phase motoroperation. It will be noted that there is a switch 165 in the upper partof the timing circuit which puts the resistances 167 and 169 isparallel. The switch 165 is provided in order to manually raise theplummet to check the system operation.

A different type probe or plummet 179 may be used with the lastdescribed mechanical device in order to provide a means for reading bothsolid and liquid levels, conductive and non-conductive, and withslightly modified logic circuitry to accomplish the electronic controls.The probe 179 is shown in FIG. 6. Mounted for insertion into the probe179 is the plunger 173. Plunger 173 has a permanent magnet 175 mountedin its upper section and has a float 171 mounted on its lower section.If the probe is to be used for measuring solid materials the float 171of course will be a weight. The plunger 173 is mounted in the channel177 for movement upward and downward within that channel. Mounted alongside the channel 177 in the probe 179 is a lower reed switch 181 and anupper reed switch 183.

If the probe 179 is to be used to measure the level of solid material,then the probe is lowered as was described in connection with the probe101 when the weight 171 comes in contact with the level of the solid,the plunger 173 is moved upward in the channel 177 so as to close thecontacts of the reed switch 181. The closing of the contacts of the reedswitch 181 is similar to providing ground potential at the terminal 127in FIG. 4. And hence it is apparent that this type of probe could beused in place of the probe 101 for effecting the measurement ofnon-conductive liquids or solid materials. In either case the float orthe weight would close the reed switch 181 which would provide groundpotential at the terminal 127 and the remainder of the circuit wouldoperate quite similarly.

In FIG. 5 there in shown circuitry to be used with the probe 179 whenboth the lower reed switch 181 and theupper reed switch 183 areemployed. In FIG. 5 the power signal is applied to the terminals 185 and180. When the switch 189 is closed there is current flow through thenormally closed relay contacts 191 through the normally closed relaycontacts 193, through the down winding 115 to the other side of thecircuit thereby causing the -motor 21 to rotate counterclockwise thuslowering the probe 179 as was described in connection with thedescription of the device in FIG. 3. At the same time there is currentflow through the normally closed relay contacts 191 through the solenoidwinding 119 so that the brake 25 remains opened thus permitting themotor to rotate as just described.

When the probe 179 has been lowered sufficiently far so that the float171 comes in contact with the liquid the plunger 173 will be movedupward in the channel 177 thus closing the contacts 195 of the reedswitch 181. It should be apparent from the circuitry of FIG. 5 thatthere will be power applied to the primary winding 197 of thetransformer 199 to develop a lesser voltage on the secondary winding20].

When the contacts 195 of the lower reed switch 181 are closed this willbias the silicon controlled rectifier 203 thereby causing it to conductduring the positive half cycles which are developed upon the secondarywinding 201. The positive half cycle will be defined as the voltageshown in FIG. 5 on the secondary winding 201.

When the silicon controlled rectifier 203 conducts, the relay 205 willbe energized and the capacitor 207 will be fully charged. As wasdescribed earlier during the negative half cycles the dischargeoperation of the capacitor 207 will keep the relay coil 205 energizedthereby causing the relay to be energized as long as the siliconcontrolled rectifier is conducting during the succeeding positivecycles.

When the relay 205 is energized the normally closed contacts 191 will beopened and the normally opened contacts 209 will be closed. When thenormally closed contacts 191 are opened the current flow to the downwinding 115 and to the solenoid winding 119 will be terminated. Hencethe motor 21 will stop driving the probe 179 downward and at the sametime the brake 25 will hold the take up wheel in a fixed positionthereby enabling the user to view the counter 19 and see the level ofthe liquid being monitored. As the liquid raises by virtue of additionalliquid being put into the holder or tank, the plunger 173 will movefurther into the channel 177 thereby closing the contact points of thereed switch 183. when the contact points 210 of the upper reed switch183 are closed, the silicon controlled rectifier 211 will be biased toconduct, during the positive cycles, thereby energizing the relay 213and charging the capacitor 215. Accordingly, as similarly describedearlier, the relay 213 will remain energized as long as the siliconcontrolled rectifier is conducting during the positive half cycles. Whenthe relay 213 is energized, the normally closed contacts 193 will beopened and the normally opened contacts 217 will be closed. When thenormally opened contacts 217 close, there will be current through thenormally opened contacts 217, through the normally open contacts 209 tothe up" winding 163, thereby causing the motor to rotate in a clockwisedirection thus lifting the probe 179 upward. When the probe 179 hasreached a point where the float 171 is resting on the surface of theliquid, the plunger 173 will have moved downward in the channel 177thereby opening the contacts 210 of the upper reed switch 183. When thisoccurs the silicon controlled rectifier 211 will no longer conduct onthe succeeding positive cycle and hence the normally open contacts 217will again become open and the normally closed contacts 193 will becomeclosed. However, at

this time the relay 205 is still energized and hence the normally closedcontacts 191 are open, therefore, the solenoid 119 is de-energizedthereby holding the probe at the new acquired level which can bedetermined from reading the value indicator on counter 19.

if on the other hand the liquid level should be lowered thus permittingthe plunger to fall downward in the channel 177, thus opening thecontacts 195, there would result an activation of the downward winding115. If the contacts 195 are opened the silicon controlled rectifier 203will stop conducting on the next positive cycle following thereafter,thus deenergizing the relay 205 which will permit the normally closedcontacts 191 to close, thus providing current flow through normallyclosed contacts 191, normally closed contacts 193 and the downwardwinding 115 thus causing the motor ro drive the take up wheel in acounterclockwise direction lowering the probe toward the falling liquid.

The switch 219 is for the purpose of manually operating the system tolift the probe to some predetermined level for starting or checking theoperation. It should also be understood that if the liquid is turbulentthe capacitors 207 and 215 may be increased to provide a suitable timedelay in the operation of the relays 205 and 213 thereby damping theeffect of the turbulence of the liquid.

In this case three conductors in the perforated tape are used.Additional conductors are provided in the tape to measure thetemperature of the liquid by means of a resistance bulb, thermocouple,or thermostat imbedded in the plummet. Two other probe variations canalso be used with the same circuitry in FIG. and the plummetconfiguration as in FIG. 6. In FIG. 7 contacts similar to 183 and 145,are made when the upper and lower probes 221 and 220 of plummet 222 comein contact with a conductive liquid.

In the case of a non-conducive liquid the plummet 224 shown in FIGS. 8and 9 can be employed. Two pendular contacts 225 and 226 are provided toengage cylindrical conductive sleeves 227 and 228. The plummet 224 is aball and rotates as it becomes buoyant and is lowered into the liquid tobe measured.

1 claim: 1. A system for monitoring a level of material held in areceptacle comprising in combination:

probe means; flexible support means comprising a perforated tapeconnected to support said probe means and formed to engage readoutmeans; readout means engaged with said perforated tape driven directlyin response to said probe means moving downwardly and upwardly in saidreceptable; take-up means coupled to said flexible support means andadapted to move said flexible support means in a first direction in saidreceptacle and alternatively to move said flexible support means in asecond direction in said receptacle; brake means coupled to said take-upmeans to hold said take-up means stationary when said brake means isactivated; and control circuit means for raising said probe means andlowering said probe means for level monitoring including first controlcircuit means including a first switching means connected theretocoupled to said take-up means and said brake means to enable saidtake-up means to move said flexible support means in a first directionuntil said first switching means is turned on responsive to a levelcondition to energize said first switching means which terminates themovement of said take-up means in said first direction whereby saidreadout means will make available the value of the level of the materialbeing monitored when said probe is not moving in either said first orsaid second directions, and second control circuit means including asecond switching means coupled to said take-up means and said brakemeans to enable said take-up means to move said flexible support meansand said probe means in a second direction for a predetermined timeuntil said second switching means is turned on thereby enabling thetermination of the movement of said take-up means in said seconddirection and reversing the movement to a movement in said firstdirection. 2. A system for monitoring the level of material according toclaim 1 wherein said flexible support means includes electricallyconductive means and wherein said probe means is an electricallyconductive means and is electrically connected to said flexible supportmeans and wherein said take-up means includes means connecting said 7 isconnected to said first switching means and wherein said housing meansis connected to said first potential whereby when said probe means comesin contact with a conductive liquid said silicon controlled rectifierwill be biased for conduction thereby said second switching meanscomprises a second silicon controlled rectifier connected to said secondcapacitor and further connected to said second circuit such that whensaid first switching means is energizing said first switching means,energized thereby closing the said normally 4 A t m f m it i a l l f i lopened closures associated therewith said second di to l i 3 h icapacitor will commence having a charge said first switching means isnormally open and developed thereon and when Said Charge is slimwhereinsaid second control circuit includes a first Ciemly great Said SecondSilicon controlled rectificapacitor connected through said lastmentioned erlwm commeflceito ct thereby energizing normally open circuiton one Side and through sa d second switching means which in turn causesZener diode and a second silicon controlled rectifirst mehhohed hh 9FIOSUreS toibh fier on Said other Side and wherein open therebyde-energizmg said first switching the anode of said last mentionedsilicon controlled 15 means rectifier is connected to said .secondswitching System, for momthrmg the level of mammals cording to claim 6wherein means whereby when said first switching means is saidtake-up-means includes a motor having at least energized said firstcapacitor commences to first and second windings and a capacitor, saidcharge until such time as there is sufficient charge capacitor connectedwith said first winding driving developed thehehcross to cause a se condslhcfm said motor in a direction to lower said probe and cohhohedrechfier 9 conduct by h f said capacitor connected to said secondwinding through Sa 1d zeher thereby eherglzlhg Sald driving said motorin a direction to lift said probe second switching means. v and whereinA system for mohhohhg the level of mateha] there is circuitry connectedto said first and second cording to Claim 4 wherein v windings includingnormally closed closures of said take'up means includes a motor havingat least said first switching means whereby while said first first andwindings and aicapacitori sflid capacitor is being charged said take-upmeans will capacitor being Connected to 531d first Windmg rotate in adirection to lift said probe and whereucausing Said motor to rotate inSuch a manner as to pon the energization of said first switching meansdrive said probe downward and said capacitor conwill open said lastmentioned normally closed connected to said second winding causing saidmotor tacts permitting said take-up means to lower said to drive so asto pull said probe upward and probe by the force of gravity for as longa period of wherein there is circuitry connected to said first time asit takes to energize said second switching and second windings includingswitching closures means- 7 associated i id fi t d second i hi 8. Asystem for monitoring the level of materials acmeans such that whenneither switching means is cording to claim 1 wherein energized saidmotor will be driving said probe Said Probe means includes a Plungermeans having a downward and when said first switching means is permanentmagnet in the upper Portion thereof energized certain of Said switchingclosures and wherein said probe means further includes sociatedtherewith will be open and certain others I first and Second reedswhchhs (hsposed h that will be closed to terminate said downwardmovewhen f Comes. In Contact with the merit and simultaneously causesaid brake means T h to be mohhored h plhhgehwhadvahce to hold saidtake-up means stationary and whereby Sald probe m .proxlmlty of saldfirs.t i when said second switching means becomes enerswitch therebyclhsmg h comact Sam first d certain of Said other switchin closures Wmreed switch to activate said first switching means glze g and whereby ifthe level of said material increases be open and certain of said otherswitching closaid plunger will advance further into said probe to sureswill be closed causing said motor to rotate so close the contacts ofsaid second reed switch as to puh Bald flexlble support means and Saidthereby activating said second control circuit. probe upwards 9. Asystem for monitoring the level of material ac- 6. A system formonitoring the level of material according to claim 8 wherein cording Fclahh l whe reih i said first switching means comprises a first siliconsaid first control circuit includes a first capacitor controlledrectifier whose control element and whose charge Passes h normally anodeelement are connected across said first reed closed clofhres of andSecond Swhchmg means switch and whose cathode is connected to said firstand switching means whereby when said first reed said first switchingmeans comprises a first silicon switch is closed said first siliconcontrolled rectificontrolled rectifier connected to said firstcapaciconducts thereby energizing Said first Switching tor and to saidfirst switching means such that means and whereby Said Second switchingmeans when there is a sufficient charge developed on Said comprises asecond silicon controlled rectifier capacitor said first siliconcontrolled rectifier will whose control element d anode are connectedconduct thereby energizing said first switching across said second reedswitch and whose cathode means and wherein is connected to said secondswitching means said second control circuit includes a second capacitorconnected through the normally open closures of said first switchingmeans and wherein whereby when said second reed switch is closed saidsecond silicon controlled rectifier conducts thereby energizing saidsecond switching means.

10. A system for monitoring the level of material according to claim 9wherein said take-up means includes a motor having first and connectedto said first winding of said motor will be energized to drive saidprobe downward and whereby when said first switching means is enersecondwindings and a capacitor wherein said gized the movement of said take-upmeans capacitor connected to said first winding will cause downward willbe terminated and Said brake i P means to rotate m one 1 means will holdsaid-take-up means stationary and said capacitor connected to saidsecond winding whereby when said second switching means IS will causesa1d take-up means to rotate in a second energized sa1d capacitorconnected to said second direction and wherein there is circuitryconnected b i d to said first and second windings including norl0 Wm mge energlz? to cause Sal i to mally open and normally closed closures ofsaid l upward z md sald brake means be first and second switching meanssuch that when re eased to perm sa1d movement either switching means isenergized said capacitor

1. A system for monitoring a level of material held in a receptaclecomprising in combination: probe means; flexible support meanscomprising a perforated tape connected to support said probe means andformed to engage readout means; readout means engaged with saidperForated tape driven directly in response to said probe means movingdownwardly and upwardly in said receptable; take-up means coupled tosaid flexible support means and adapted to move said flexible supportmeans in a first direction in said receptacle and alternatively to movesaid flexible support means in a second direction in said receptacle;brake means coupled to said take-up means to hold said take-up meansstationary when said brake means is activated; and control circuit meansfor raising said probe means and lowering said probe means for levelmonitoring including first control circuit means including a firstswitching means connected thereto coupled to said take-up means and saidbrake means to enable said take-up means to move said flexible supportmeans in a first direction until said first switching means is turned onresponsive to a level condition to energize said first switching meanswhich terminates the movement of said take-up means in said firstdirection whereby said readout means will make available the value ofthe level of the material being monitored when said probe is not movingin either said first or said second directions, and second controlcircuit means including a second switching means coupled to said take-upmeans and said brake means to enable said take-up means to move saidflexible support means and said probe means in a second direction for apredetermined time until said second switching means is turned onthereby enabling the termination of the movement of said take-up meansin said second direction and reversing the movement to a movement insaid first direction.
 2. A system for monitoring the level of materialaccording to claim 1 wherein said flexible support means includeselectrically conductive means and wherein said probe means is anelectrically conductive means and is electrically connected to saidflexible support means and wherein said take-up means includes meansconnecting said flexible support means to said first and second controlcircuit means.
 3. A system for monitoring the level of material held insaid receptacle according the claim 2 wherein said first switching meanscomprises a silicon controlled rectifier whose anode is connected to afirst potential and whose control element is connected to said flexiblesupport means and whose cathode is connected to said first switchingmeans and wherein said housing means is connected to said firstpotential whereby when said probe means comes in contact with aconductive liquid said silicon controlled rectifier will be biased forconduction thereby energizing said first switching means.
 4. A systemfor monitoring a level of material according to claim 3 wherein saidfirst switching means is normally open and wherein said second controlcircuit includes a first capacitor connected through said last mentionednormally open circuit on one side and through a Zener diode and a secondsilicon controlled rectifier on said other side and wherein the anode ofsaid last mentioned silicon controlled rectifier is connected to saidsecond switching means whereby when said first switching means isenergized said first capacitor commences to charge until such time asthere is sufficient charge developed thereacross to cause a secondsilicon controlled rectifier to conduct by virtue of bias through saidZener diode, thereby energizing said second switching means.
 5. A systemfor monitoring the level of material according to claim 4 wherein saidtake-up means includes a motor having at least first and second windingsand a capacitor, said capacitor being connected to said first windingcausing said motor to rotate in such a manner as to drive said probedownward and said capacitor connected to said second winding causingsaid motor to drive so as to pull said probe upward and wherein there iscircuitry connected to said first and second windings includingswitching closures associated with said first and second switching meanssuch that when neither switching means is energized said motor will bedriving said probe downward and when said first switching means isenergized certain of said switching closures associated therewith willbe open and certain others will be closed to terminate said downwardmovement and simultaneously cause said brake means to hold said take-upmeans stationary and whereby when said second switching means becomesenergized certain of said other switching closures will be open andcertain of said other switching closures will be closed causing saidmotor to rotate so as to pull said flexible support means and said probeupwards.
 6. A system for monitoring the level of material according toclaim 1 wherein said first control circuit includes a first capacitorwhose charge circuit passes through the normally closed closures of saidsecond switching means and wherein said first switching means comprisesa first silicon controlled rectifier connected to said first capacitorand to said first switching means such that when there is a sufficientcharge developed on said capacitor said first silicon controlledrectifier will conduct thereby energizing said first switching means andwherein said second control circuit includes a second capacitorconnected through the normally open closures of said first switchingmeans and wherein said second switching means comprises a second siliconcontrolled rectifier connected to said second capacitor and furtherconnected to said second circuit such that when said first switchingmeans is energized thereby closing the said normally opened closuresassociated therewith said second capacitor will commence having a chargedeveloped thereon and when said charge is sufficiently great said secondsilicon controlled rectifier will commence to conduct thereby energizingsaid second switching means which in turn causes said first mentionednormally closed closures to be open thereby de-energizing said firstswitching means.
 7. A system for monitoring the level of materialsaccording to claim 6 wherein said take-up means includes a motor havingat least first and second windings and a capacitor, said capacitorconnected with said first winding driving said motor in a direction tolower said probe and said capacitor connected to said second windingdriving said motor in a direction to lift said probe and wherein thereis circuitry connected to said first and second windings includingnormally closed closures of said first switching means whereby whilesaid first capacitor is being charged said take-up means will rotate ina direction to lift said probe and whereupon the energization of saidfirst switching means will open said last mentioned normally closedcontacts permitting said take-up means to lower said probe by the forceof gravity for as long a period of time as it takes to energize saidsecond switching means.
 8. A system for monitoring the level ofmaterials according to claim 1 wherein said probe means includes aplunger means having a permanent magnet in the upper portion thereof andwherein said probe means further includes first and second reed switchesdisposed such that when said plunger comes in contact with the materialto be monitored said plunger will advance into said probe in proximityof said first reed switch thereby closing the contacts of said firstreed switch to activate said first switching means and whereby if thelevel of said material increases said plunger will advance further intosaid probe to close the contacts of said second reed switch therebyactivating said second control circuit.
 9. A system for monitoring thelevel of material according to claim 8 wherein said first switchingmeans comprises a first silicon controlled rectifier whose controlelement and anode element are connected across said first reed switchand whose cathode is connected to said first switching means wherebywhen said first reed switch is closed said first silicon controlleDrectifier conducts thereby energizing said first switching means andwhereby said second switching means comprises a second siliconcontrolled rectifier whose control element and anode are connectedacross said second reed switch and whose cathode is connected to saidsecond switching means whereby when said second reed switch is closedsaid second silicon controlled rectifier conducts thereby energizingsaid second switching means.
 10. A system for monitoring the level ofmaterial according to claim 9 wherein said take-up means includes amotor having first and second windings and a capacitor wherein saidcapacitor connected to said first winding will cause said take-up meansto rotate in one direction and said capacitor connected to said secondwinding will cause said take-up means to rotate in a second directionand wherein there is circuitry connected to said first and secondwindings including normally open and normally closed closures of saidfirst and second switching means such that when either switching meansis energized said capacitor connected to said first winding of saidmotor will be energized to drive said probe downward and whereby whensaid first switching means is energized the movement of said take-upmeans downward will be terminated and said brake means will hold saidtake-up means stationary and whereby when said second switching means isenergized said capacitor connected to said second winding will beenergized to cause said motor to move upward and said brake means willbe released to permit said movement.